In recent years, cooking devices such as an induction cooking device for induction heating a cooking container such as a pan with a heating coil and a gas cooking device for heating the cooking container with gas are widely used in general household and professional-use kitchens. Some of these heating cooking devices include an operation unit such as a touch key on an upper surface of a top plate (see e.g., patent documents 1 to 3).
The operation unit of patent document 1 includes one or more electrostatic capacitance touch keys. The touch key is a pair of key electrodes provided on the upper surface and the lower surface of the top plate. The key electrode on the lower surface side of the top plate is electrically connected to a contact electrode. The contact electrode is contacted with an end of a conductive connection member connected to a control unit. The control unit outputs a high frequency signal to the key electrode via the connection member and measures the magnitude of the signal output to the key electrode. When a finger of a user touches the touch key, the reduction of the magnitude of the high frequency signal output to the key electrode is transmitted to the control unit through the contact electrode and the connection member in correspondence to the increase in the electrostatic capacitance with respect to the earth of the key electrode (e.g., FIGS. 4 to 6 of patent document 1).
In the cooking device of patent document 2, an operation circuit substrate in which a planar electrode is formed with copper foil is provided on the lower side of the top plate, and a shield electrode connected to a common potential of a circuit for detecting the operation signal is provided at the periphery of the planar electrode to ensure the contacting range of the touch key. Thus, when the vicinity of the outer edge of the planar electrode is touched, the planar electrode and the vicinity of the shield electrode are both contacted, and thus the potential of the planar electrode lowers and the touch key can be easily operated.
In the cooking device of patent document 3, heating does not start if an object is placed on the periphery of the operation unit to enhance safety. Specifically, a peripheral state detection means for detecting whether an object is placed thereon is provided in the vicinity of the operation unit. Heating does not start if the peripheral state detection means detects that the object is placed on the peripheral state detection means.
Patent document 1: JP-A-2003-303673
Patent document 2: JP-A-10-214677
Patent document 3: JP-A-2006-207843